An argument has broken out over whether or not a barrel that looks to be about half full more or less than half full. Without any measuring devices (like a ruler, yardstick, measuring cup, etc.) how can the it be easily determined if the barrel is more or less than half full? The barrel has no lid and no rum was taken out.

You could mark the current level of the rum, then put a lid on the barrel, flip it over, and open it up on the other end. If the level of the rum at that point is lower than the mark, it means that the barrel is less than half full. However, if the level of the rum passes the mark, the barrel is over half full.

Tip the barrel until the rum is both touching the lip of the barrel, as well as just managing to cover the entire bottom portion.. it's hard to explain without a diagram (I assume you know what I'm talking about, if not I'll scan it in). If some water pours out before you get to this point, you had over half... if it can't reach that point, you have less.

Tipping the barrel until the rum reaches the lip and looking to see if you can see the bottom of the barrel. If you can see the bottom of the barrel, then it is less than half full. If the bottom of the barrel is not yet visible, then the barrel is more than half full!